有A、B、C、D四种物质。A是无色无味的气体．B在A中燃烧发出明亮的蓝紫色火焰，同时生成一种无色有刺激气味的气体C。D是一种无色的气体，纯净的D气体能在空气中安静的燃烧，发出淡蓝色火焰。试判断A、B、C、D各是什么物质，请将物质名称填在空格内。

A是____；B是____；C是____；D是____。

解释下列词语

集思广益： ____

辗转反侧： ____

熠熠发光： ____

如图，⊙O与⊙P相交于A，B两点，点P在⊙O上，⊙O的弦BC切⊙P于点B，CP及其延长线交⊙P于D，E两点，过点E作EF⊥CE交CB延长线于点F．若CD=2，CB=2$\sqrt{2}$，则EF的长为(    )

    This is Mary's family. After dinner, Mary's mother talks on the phone. Mary's father watches TV. Mary's grandfather reads books. Mary's brother draws a picture. Mary plays with her teddy bear. They are a happy family.

⑴Mary's mother ____          A.

⑵Mary's father ____           B.

⑶Mary's grandfather ____      C.

⑷Mary's brother ____         D.

⑸Mary ____                 E.